Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells ...
Supporting Information
Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells: Charge Transport, Recombination, and Diffusion Length Yixin Zhao, Alexandre M. Nardes, and Kai Zhu* Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401
Experimental Method Transparent conducting substrate. Fluorine-doped transparent conducting SnO2-coated glass substrate (FTO; TEC15, Hartford, USA) was pre-patterned by etching with Zn powder and 25 wt% HCl solution for about two min. The patterned FTO substrate was then cleaned by soaking in 5 wt% NaOH in alcohol for 16 h and then rinsing it sequentially with deionized (DI) water and ethanol. The cleaned FTO substrate was subsequently coated with a compact TiO2 layer by spray pyrolysis using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide in 1-butanol solution at 450°C, followed by annealing at 450°C for 1 h.1 Mesoporous TiO2 film. The 20-nm-sized TiO2 nanoparticles were synthesized by following previous reports.2-3 Various TiO2 pastes with different weight percentages (3–18 wt%) of the 20-nm TiO2 nanoparticles mixed with terpineol and ethyl cellulose were screen-printed on the patterned FTO substrates to produce TiO2 films with average film thickness ranging from 240–1650 nm. The thickness is controlled by using TiO2 paste with different weight percentage of TiO2 nanoparticles. The emulsion thicknesses of the screens were also adjusted. The printed mesoporous TiO2 film was annealed at 500°C for 0.5 h. The TiO2 films were then soaked in 0.04 M TiCl4 solution at 65°C for 0.5 h, followed by rinsing with DI water and ethanol, and finally dried under N2. These TiCl4-treated TiO2 films were annealed again at 500°C for 0.5 h before the deposition of perovskite CH3NH3PbI3 absorber or uptake of Z907 dye molecules. Device fabrication. For perovskite solar cells, the perovskite CH3NH3PbI3 coating was done by spin coating as detailed in our previous report.4 In brief, the perovskite CH3NH3PbI3 was deposited on the mesoporous TiO2 film by spin coating with a stoichiometric CH3NH3I and PbI2 solution in γbutyrolactone. CH3NH3I was synthesized by reacting methylamine (33 wt% ethanol solution) and hydroiodic acid (57 wt% in water, Aldrich) with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring. The precipitate was first dried by a rotary evaporator, followed by repeated washing and centrifuging with ethyl acetate until no yellow residue remains, and finally dried under vacuum. 1.157 g PbI2 and 0.395 g CH3NH3I were dissolved in 2.0 mL γ-butyrolactone solution at 60°C. The clear 1
perovskite precursor solution was first spread on the TiO2 substrate for 5 s and then was spun at 2000 rpm for 30 s in ambient condition. The deposited CH3NH3PbI3 film was finally dried on a hotplate at 100°C for 5 min. For dye-sensitized solar cells, the TiO2 films were immersed in tert-butyl alcohol/acetonitrile (1:1, v/v) containing 0.3 mM Ru(4,4’-dicarboxylic acid-2,2’-bipyridine)(4,4’dinonyl-2,2’-bipyridine)(NCS)2 (Z907) for 16 h at room temperature. For both perovskite solar cells and dye-sensitized solar cells, a hole transport material (HTM) solution was spin-coated on the sensitized TiO2 electrodes at 4000 rpm for 30 s. The HTM solution consists of 0.15 M 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiroMeOTAD), 0.05 M bis(trifluoromethane)sulfonimide lithium salt (Li-TFSi), and 0.18 M 4-tertbutylpyridine (tBP) in chlorobenzene/acetonitrile (10:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. The active area of each device was about 0.15–0.28 cm2. Characterization. The crystal structures of the perovskite films were measured by X-ray diffraction (XRD, Rigaku D/Max 2200 diffractometer with Cu Kα radiation). The absorption spectra of the perovskite films were characterized by an UV/Vis-NIR spectrophotometer (Cary-6000i). The photocurrent–voltage characteristic of solid-state mesostructured perovskite cells and dye-sensitized solar cells were measured with a Keithley 2400 source meter under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). The performance data of perovskite solar cells are representative from 12–20 cells (unless otherwise stated) for each TiO2 film thickness. Charge transport and recombination properties of the perovskite sensitized cells were measured by intensitymodulated photocurrent and photovoltage spectroscopies as described previously.5
Figure S1. (a) X-ray diffraction patterns of the TiO2/FTO substrate and perovskite CH3NH3PbI3 deposited on the TiO2/FTO substrate. (b) UV-vis absorption spectra of perovskite CH3NH3PbI3 as a function of TiO2 film thickness.
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Figure S2. (a) Effect of TiO2 film thickness on the J–V curves of mesostructured perovskite CH3NH3PbI3 solar cells. (b) Dependence of Jsc on the TiO2 film thickness. The error bars represent the measurements from 12–20 cells. The solid line in (b) is a fitting to a simple model J sc ∝ 1 − exp(− αd ) assuming constant charge-collection efficiency for all thickness (d) and an effective absorption coefficient (α). This simple model fits well for all samples except for the one with the thickest TiO2 film (1.65 µm). The effective absorption length (1/α) from the fitting is about 250 nm.
Figure S3. Effect of TiO2 film thickness on the IPCE spectra of mesostructured perovskite CH3NH3PbI3 solar cells.
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Figure S4. J–V and IPCE curves of an optimized solid-state mesostructured perovskite CH3NH3PbI3 solar cell using a 650-nm TiO2 film. The cell efficiency is 10.3% with a Jsc of 17.8 mA/cm2, Voc of 0.90 V, and FF of 0.64.
Figure S5. (a) UV-vis absorption spectrum and (b) J–V (inset: IPCE) of solid-state Z907 dye-sensitized solar cells using 650-nm-thick TiO2 films.
REFERENCES (1). Jang, S. R.; Zhu, K.; Ko, M. J.; Kim, K.; Kim, C.; Park, N. G.; Frank, A. J. Voltage-enhancement mechanisms of an organic dye in high open-circuit voltage solid-state dye-sensitized solar cells. ACS Nano 2011, 5, 8267–8274. (2). Neale, N. R.; Frank, A. J. Size and shape control of nanocrystallites in mesoporous TiO2 films. J. Mater. Chem. 2007, 17, 3216–3221. (3). Ito, S.; Murakami, T. N.; Comte, P.; Liska, P.; Gratzel, C.; Nazeeruddin, M. K.; Gratzel, M. Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%. Thin Solid Films 2008, 516, 4613–4619. (4). Zhao, Y.; Zhu, K. Charge transport and recombination in perovskite (CH3NH3)PbI3 sensitized TiO2 solar cells. J. Phys. Chem. Lett. 2013, 4, 2880–2884. (5). Zhu, K.; Kopidakis, N.; Neale, N. R.; van de Lagemaat, J.; Frank, A. J. Influence of surface area on charge transport and recombination in dye-sensitized TiO2 solar cells. J. Phys. Chem. B 2006, 110, 25174–25180.
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Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells: Charge Transport, Recombination, and Diffusion Length Yixin Zhao, Alexandre M. Nardes, and Kai Zhu* Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401
Experimental Method Transparent conducting substrate. Fluorine-doped transparent conducting SnO2-coated glass substrate (FTO; TEC15, Hartford, USA) was pre-patterned by etching with Zn powder and 25 wt% HCl solution for about two min. The patterned FTO substrate was then cleaned by soaking in 5 wt% NaOH in alcohol for 16 h and then rinsing it sequentially with deionized (DI) water and ethanol. The cleaned FTO substrate was subsequently coated with a compact TiO2 layer by spray pyrolysis using 0.2 M Ti(IV) bis(ethyl acetoacetate)-diisopropoxide in 1-butanol solution at 450°C, followed by annealing at 450°C for 1 h.1 Mesoporous TiO2 film. The 20-nm-sized TiO2 nanoparticles were synthesized by following previous reports.2-3 Various TiO2 pastes with different weight percentages (3–18 wt%) of the 20-nm TiO2 nanoparticles mixed with terpineol and ethyl cellulose were screen-printed on the patterned FTO substrates to produce TiO2 films with average film thickness ranging from 240–1650 nm. The thickness is controlled by using TiO2 paste with different weight percentage of TiO2 nanoparticles. The emulsion thicknesses of the screens were also adjusted. The printed mesoporous TiO2 film was annealed at 500°C for 0.5 h. The TiO2 films were then soaked in 0.04 M TiCl4 solution at 65°C for 0.5 h, followed by rinsing with DI water and ethanol, and finally dried under N2. These TiCl4-treated TiO2 films were annealed again at 500°C for 0.5 h before the deposition of perovskite CH3NH3PbI3 absorber or uptake of Z907 dye molecules. Device fabrication. For perovskite solar cells, the perovskite CH3NH3PbI3 coating was done by spin coating as detailed in our previous report.4 In brief, the perovskite CH3NH3PbI3 was deposited on the mesoporous TiO2 film by spin coating with a stoichiometric CH3NH3I and PbI2 solution in γbutyrolactone. CH3NH3I was synthesized by reacting methylamine (33 wt% ethanol solution) and hydroiodic acid (57 wt% in water, Aldrich) with the molar ratio of 1.2:1 in an ice bath for 2 h with stirring. The precipitate was first dried by a rotary evaporator, followed by repeated washing and centrifuging with ethyl acetate until no yellow residue remains, and finally dried under vacuum. 1.157 g PbI2 and 0.395 g CH3NH3I were dissolved in 2.0 mL γ-butyrolactone solution at 60°C. The clear 1
perovskite precursor solution was first spread on the TiO2 substrate for 5 s and then was spun at 2000 rpm for 30 s in ambient condition. The deposited CH3NH3PbI3 film was finally dried on a hotplate at 100°C for 5 min. For dye-sensitized solar cells, the TiO2 films were immersed in tert-butyl alcohol/acetonitrile (1:1, v/v) containing 0.3 mM Ru(4,4’-dicarboxylic acid-2,2’-bipyridine)(4,4’dinonyl-2,2’-bipyridine)(NCS)2 (Z907) for 16 h at room temperature. For both perovskite solar cells and dye-sensitized solar cells, a hole transport material (HTM) solution was spin-coated on the sensitized TiO2 electrodes at 4000 rpm for 30 s. The HTM solution consists of 0.15 M 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiroMeOTAD), 0.05 M bis(trifluoromethane)sulfonimide lithium salt (Li-TFSi), and 0.18 M 4-tertbutylpyridine (tBP) in chlorobenzene/acetonitrile (10:1, v/v) solution. Finally, a 150-nm-thick Ag layer was deposited on the HTM layer by thermal evaporation. The active area of each device was about 0.15–0.28 cm2. Characterization. The crystal structures of the perovskite films were measured by X-ray diffraction (XRD, Rigaku D/Max 2200 diffractometer with Cu Kα radiation). The absorption spectra of the perovskite films were characterized by an UV/Vis-NIR spectrophotometer (Cary-6000i). The photocurrent–voltage characteristic of solid-state mesostructured perovskite cells and dye-sensitized solar cells were measured with a Keithley 2400 source meter under the simulated AM 1.5G illumination (100 mW/cm2; Oriel Sol3A Class AAA Solar Simulator). The performance data of perovskite solar cells are representative from 12–20 cells (unless otherwise stated) for each TiO2 film thickness. Charge transport and recombination properties of the perovskite sensitized cells were measured by intensitymodulated photocurrent and photovoltage spectroscopies as described previously.5
Figure S1. (a) X-ray diffraction patterns of the TiO2/FTO substrate and perovskite CH3NH3PbI3 deposited on the TiO2/FTO substrate. (b) UV-vis absorption spectra of perovskite CH3NH3PbI3 as a function of TiO2 film thickness.
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Figure S2. (a) Effect of TiO2 film thickness on the J–V curves of mesostructured perovskite CH3NH3PbI3 solar cells. (b) Dependence of Jsc on the TiO2 film thickness. The error bars represent the measurements from 12–20 cells. The solid line in (b) is a fitting to a simple model J sc ∝ 1 − exp(− αd ) assuming constant charge-collection efficiency for all thickness (d) and an effective absorption coefficient (α). This simple model fits well for all samples except for the one with the thickest TiO2 film (1.65 µm). The effective absorption length (1/α) from the fitting is about 250 nm.
Figure S3. Effect of TiO2 film thickness on the IPCE spectra of mesostructured perovskite CH3NH3PbI3 solar cells.
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Figure S4. J–V and IPCE curves of an optimized solid-state mesostructured perovskite CH3NH3PbI3 solar cell using a 650-nm TiO2 film. The cell efficiency is 10.3% with a Jsc of 17.8 mA/cm2, Voc of 0.90 V, and FF of 0.64.
Figure S5. (a) UV-vis absorption spectrum and (b) J–V (inset: IPCE) of solid-state Z907 dye-sensitized solar cells using 650-nm-thick TiO2 films.
REFERENCES (1). Jang, S. R.; Zhu, K.; Ko, M. J.; Kim, K.; Kim, C.; Park, N. G.; Frank, A. J. Voltage-enhancement mechanisms of an organic dye in high open-circuit voltage solid-state dye-sensitized solar cells. ACS Nano 2011, 5, 8267–8274. (2). Neale, N. R.; Frank, A. J. Size and shape control of nanocrystallites in mesoporous TiO2 films. J. Mater. Chem. 2007, 17, 3216–3221. (3). Ito, S.; Murakami, T. N.; Comte, P.; Liska, P.; Gratzel, C.; Nazeeruddin, M. K.; Gratzel, M. Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%. Thin Solid Films 2008, 516, 4613–4619. (4). Zhao, Y.; Zhu, K. Charge transport and recombination in perovskite (CH3NH3)PbI3 sensitized TiO2 solar cells. J. Phys. Chem. Lett. 2013, 4, 2880–2884. (5). Zhu, K.; Kopidakis, N.; Neale, N. R.; van de Lagemaat, J.; Frank, A. J. Influence of surface area on charge transport and recombination in dye-sensitized TiO2 solar cells. J. Phys. Chem. B 2006, 110, 25174–25180.
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